Simon LeVay, a neuroscientist at the Salk
Institute in San Diego
has found that in homosexual men, part of the anterior hypothalamus (a brain region that governs sexual behavior) has the
anatomical form in size usually found in women rather than the form typically of heterosexual men. This difference found in
the brains between homosexuals and heterosexuals raises the possibility that this difference may not only correlate with homosexuality
but may also be the cause of it.
At the same time, the research team of
Roger Gorski at the University of California, Los Angeles, had examined post-mortem human brains and found two regions, or
“nuclei,” in the anterior hypothalamus that are more than twice as large in men as they are in women. LeVay extended
this study onto homosexual men, using brains of men who had died of AIDS and other diseases. In his results, in most of the
19 homosexuals (with mean age of 38.2) he looked at, he found that one of these nuclei called INAH-3 (the third interstitial
notch of the anterior hypothalamus), was smaller than it is in heterosexual men and in fact, it was the same size as it is
in a typical heterosexual woman.